Problem-Solving and Data AnalysisMediumTwo blue draws with replacement
Problem-Solving and Data Analysis practice question
A bag contains 5 red marbles and 3 blue marbles. One marble is drawn at random and put back, and then a second marble is drawn at random. What is the probability that both marbles drawn are blue?
Answer: 9/64
Each draw has probability 3/8 of blue, and the draws are independent: (3/8)² = 9/64.
Common wrong answers
- If you answered 3/28
- 3/28 treats the draws as without replacement.
- If you answered 3/8
- 3/8 is the probability of one blue draw.
- If you answered 6/16
- 6/16 adds the probabilities instead of multiplying.
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